1. Field of the Invention
The present invention relates to a pump housing and manufacturing method therefor, and more particularly to a pump housing and manufacturing method therefor, wherein a molding process of a pump housing for circulating hot water is separated into a primary molding and a second molding for improving quality of a product and reducing manufacturing Cost.
2. Description of the Prior Art
A pump housing of a hot-water circulating pump molded via a conventional molding method is illustrated in FIGS. 1 and 2. FIG. 1 is a plan view showing the pump housing, and FIG. 2 is a sectional view thereof.
As shown in FIGS. 1 and 2, pump housing 10 has an inlet 15 for admitting a fluid, and a volute chamber 11 formed for facilitating the flowing of the admitted fluid and constantly maintaining the sum of ordinary flow rate components and an outlet 13 for discharging the admitted fluid. A whirlpool-type spiral groove 17 is formed within volute chamber 11. The pump housing 10 cannot be formed by a single injection molding process due to the shape of spiral groove 17 and the streamlined structure of the inlet 15 and outlet 13. Therefore, a core which is a hollow bar of a metal mold is employed to perform the molding, and then removed after the molding.
FIG. 3 illustrates a process for manufacturing pump housing 10 via the conventional molding method. Referring to FIG. 3, a metal mold fabricating step for forming a metal mold having the outer surface shape of pump housing 10 and a core fabricating step for forming a core constituting the interior of inlet 15, outlet 13 and volute chamber 11 should be executed in advance.
After finishing the above steps, a core installing step for installing the core within the fabricated metal mold, and an injection molding step are sequentially carried out. After the injection molding, pump housing 10 is separated from the metal mold, and a core removing step of eliminating the core within pump housing 10 is then executed. Thus, the molding process of pump housing 10 is completed to produce completed pump housing 10.
The core removing process is different depending upon the type of core being used. That is, a lost core for removing the core after injection-molding pump housing 10 is classified into a casting sand lost core which uses casting sand during a casting for pulverizing to remove the core after the injection molding and a messed lost core which injects an alloy of lead and bismuth during the injection molding for melting to remove the alloy after the injection molding.
The molding method of the pump housing using the lost core involves steps of the metal mold fabrication, core fabrication, core installation, injection molding and core removal to require relatively lengthy processing. In particular, the removal step has drawbacks since this step require a long time to be completed and also requires a highly skilled worker.
That is, with regard to the injection molding, the messed is a lead-bismuth alloy in which heat is applied in order to remove the alloy after the injection molding. This process result in much time and labor so the operation is costly. Due to the aforesaid drawback, injection molding is only applied to special use products rather than general use products.
Also, in case of the casting, the casting sand lost core is broken or pulverized to be removed after the casting. Thus, so much time is required and the working is difficulty.
Additionally, in overall molding process, the lost core installed to the metal mold is liable to be shaken while a liquid metal is poured to be forced out or inclined toward one side. Particularly, the casting is disadvantageous in that the lost core is moved while the casting sand is broken down. Furthermore, in spite that a core bar is inserted into the core for preventing the warping of the lost core, the lost core is warped to be deformed owing to the high temperature of the liquid metal which in turn results in a defect of products.